<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
<style type="text/css">
</style>
<script type="text/javascript" src="../static/knockout-3.3.0.js">
	
</script>
</head>
<body>
	<div data-bind="style:{color:showWarn()<0?'red':'black'}">hello</div>
	<button onclick="deplus()">dsaf</button>
</body>
<script type="text/javascript">
	var myViewModel = {
		showWarn : ko.observable(100)
	}
	function deplus() {
		myViewModel.showWarn(-1);
	}
	ko.applyBindings(myViewModel);
</script>
</html>